Perhaps this has already been covered, but what will happen to our forum inventories once the new mod is released. Will all items carry over? Will we be refunded the cost and all items deleted? Will they all just be flat out deleted?

If you purchased a game from steam that was extremely complex and difficult, with no in game tutorial, most people are more likely to refund it and never pick it up again than spend 2 hours of googling gathering scraps of out of context information here and scraps of out of context information there. Thinking they're retarded and deserve it for not doing the latter is very narrow thinking. At the end of the day they lose nothing from uninstalling and forgetting about the mod, but we sort of do.

On my first day on pw I walked up to the lannister castle, as it was the only castle I saw once I spawned, and got peppered by 4 archers. I went back to try again, same thing happened. I then ran to the next castle I saw, finding a free shitty hunting bow on the way. I picked it up and continued towards the castle. I got halted by a lorraine and told to show pouch, I asked how, got killed for it. I returned for my bow, nobody picked it up since it was so shit, I picked it up, then got butchered by the same lorraine who halted me for taking it.
Then the cycle of; respawning, get told to show pouch, ask how to, get killed repeated about 6 times. However I was one of the lucky pubs and just before I ragequit, some levy showed me the basics. Not one person told me "Hey there's a forum you can check the rules out on" or "If you don't know what this module is or how to play it read this"
Most of the people who are new to PW have like 50 hours in the game (although now and again you get one who proudly exclaims "Actually I have a couple of hundred hours on mount and blade, im pretty good xD") , they either see a short youtube video and decide to try the module out or see one of the top servers has 100+ players, try to connect and see "Module not installed". They google pw 4.5, download it, join the server, and experience the exact same thing I just described until they're forced off the server because they weren't lucky enough to come across someone who isn't a cunt. It's pathetic that we even need some sort of new player protection, but if you're serious about wanting to retainin new players on the new mod, we really really do.
This is me speaking as someone who I can guarantee spends more time with new players trying to teach them than anyone else. 70% of new players quit within the same week because of this behaviour towards new players. 29% realise they can't just fuck around as outlaws because if they try to rob somebody, 30 cavalry all with 2000 hours each are going to come storming across a bridge and fuck them up, so they need to join a clan. The other 1% make it without a clan, usually as serfs.

the immense speed penalties to wearing any sort of Armour (Particularly heavy Armour) often encourage people to play naked with long reaching weapons
Unless I've missed something, what encourages people to play naked is the fact they have nothing to lose but could gain themselves armor if they manage to score a kill on someone who is isolated, bad at melee, and in tin. Not "I'm going to go to the next war naked because I think I will be more effective".
wearing heavy (and therefore expensive) sets of Armour often obsolete in a lot of skirmish type engagements
What is your definition of skirmish type engagements? Most "10 of our best vs 10 of your best" include all 20 of those players being in tin. If you're talking nakeds raiding a clan, the reason they're naked is so they can grab tin, and if they die they lose nothing so it's fine. It's hardly because being naked it just too op. See clip for evidence of this (Please excuse the cocky title): https://plays.tv/video/59be8d52942ce8519c/still-not-considered-best-archer-in-clan-?from=user
This is most noticeable with Men at Arms, who when dismounted are almost comically slow in heavy Armour
This is a class issue not an armour issue. Sergeants run 1.5x faster than men at arms in the exact same tin. You're right it is comically slow but I think that is a balancing issue, if they weren't so slow men at arms beat sergeants in everything other than the amount of hits they can take (I believe)
At the same time, light armour is hilariously ineffective and seldom ever bought, unless stocks of other Armour are dry.
Ehhhh, debatable. When raiding often the raiding party will opt in to light armour. When playing pub I pretty much always opt in for light armour. However it's use is very limited, all it really acts as is "Stops you dying in one hit to certain weapons". Naked vs light armor in a duel you could argue there isn't really much of a noticeable difference, but at the same time I think that's the point. If you want a noticeable amount of protection for a cheap price buy archer gear.
PW creates an environment where groups of nakeds, with longer reach weapons are often much more effective in combat against people in Armour, being able to kite them at will, this is more noticeable in duels.
This is only noticeable in duels, never have I seen a war with nakeds curb stomping an army of full tin with even numbers. I saw it attempted once as a sour rejection to a field battle they brung nakeds to our army of tins. This ended in two of our guys dead to ghetto lances and about 30 of theirs dead.
The only benefit being naked provides outside of very situational duels is the fact you don't lose anything if you die. I'm 100% sure if you implement a "Pay 35k from your bank every time you die" feature you'll see a lot less nakeds. Or perhaps there's just something im missing when looking at this situation and I'm actually wrong.

This I think is a matter of clans vs pubs. Clans (I presume) won't like this because it lengthens the process of stocking castles, nobody wants to be the poor guy selected to create 100 maces for the upcoming war. If this is implemented those 100 maces become 10x longer to create. However those who enjoy playing the mastersmith role, myself included, would love this. :( and we all know who wins any decision that is pubs vs clans

If you're going to make your own mod perhaps it would be best to create a new subforum similar to "support & Suggestions" where people can suggest new features for the new mod, and the community can vote on each idea?

This. When you make events solely for clan members and throw out permabans for anyone who dares consider joining in on the event, you give off the impression that pubs are in fact not part of the community. I wasn't banned nor did I take part, so personally I'd consider myself a neutral party, but the fact this has occurred is down-right pathetic. If you're going to exclude people from playing the game and permabanning them for joining a clan-only event, make a clan only server. It's retarded.

This.
However there are many other ways to reward people, for example:
Daily rewards. (x amount for killing x amount of players in an enemy faction that day, x amount for travelling x amount of distance during that day, x amount for crafting x amount of items)
Implementation of something along the lines to "Repairing x amount of damage as a mastersmith/building x amount of ladders" gives you a few k, "Healing x amount of damage as a doctor" gives you a few k, "Travelling x amount of distance if you're trained the traveller class" gives you a few k, "Sailing x amount of distance as a sailor" gives you a few k.
It all depends on what the new server side scripts can support.

surely this is just inflation of the PW economy and nothing would actually change other than lowering the value of the gold people already have in their banks, and making their current bank limit less valuable too.

Outlaws do not need to request help to be assisted by other outlaws.
The above is a great rule. It means that pub outlaws who meet up in game don't break the rules by accidentally forgetting to say help, and it also increases the fluidity of the outlaws gameplay experience. However, commoners who meet up in game and decide to play together don't have such a luxury, and this could potentially lead to new players to the server being banned, and dissuaded from ever playing Phoenix again. I also often play with newcomers, and it's frustrating watching them getting halted and killed, and not being able to help them in the situation purely because they panicked and forgot to type help in local chat. They then ragequit, never to step foot on PW_Phoenix ever again.